This application corresponds to Japanese Patent Application No. Hei 9-223582, filed on Aug. 20, 1997, which is hereby incorporated by reference in its entirety herein.
1. Field of the Invention
The present invention relates to a designing method of leadframe tip arrangement for automatically designing an arrangement of tips of a leadframe used for semiconductor packages.
2. Background Art
In a conventional leadframe tip arrangement method disclosed, for instance, in a Japanese Patent Application, Laid-Open No. 7-49894 entitled "Leadframe Tip Arrangement Designing Method", arrangement positions of leadframe tips are specified first by a cavity line, for instance, and then the leadframe tip width and interval are specified according to the same criterion, such as the same circle diameter. Therefore, it is difficult to provide proper arrangement positions, and it is also necessary to specify the leadframe tip width and interval. Further, since the leadframe tip width and interval are determined according to the same criterion, it is difficult to provide optimum values independently for those parameters.
FIG. 6 is a flowchart that is obtained by modifying a flowchart used in the above conventional leadframe tip arrangement method (Japanese Patent Application Laid-Open No. 7-49894) so that this flowchart can be correlated and compared with an algorithm of the present invention. In FIG. 6, reference symbol S1-2 denotes a design condition input step for inputting arrangement lines such as a cavity line. Symbol S4-2 denotes a leadframe tip width setting step for defining a leadframe width by a circle radius. Symbol S4-3 denotes a leadframe interval calculation step for determining center coordinates of a circle in which the leadframe is to be disposed. Since the leadframe position is determined, the leadframe interval is determined at this step. Symbol S5-2 denotes a step for judging whether the leadframe tip width and the interval fall within the ranges of the desired design conditions. Symbol S7 denotes a judgment step for checking whether the leadframe tips satisfy the design criteria. Finally, symbol S8 denotes a step for presenting design results to the user.
Next, with reference to FIG. 6, the conventional leadframe tip position determining method will be described below in further detail. First, at step S1-2, lines for specifying leadframe tip arrangement positions are input. At step S4-2, a leadframe width is set as a circle radius. At step S4-3, a leadframe interval is determined (center coordinates of the circle that was determined at step S4-2 are determined). At step S5-2, it is judged whether the tip width and interval of the leadframe, that are defined by a tangent line of the circle determined at steps S4-2 and S4-3, fall outside of the desired design conditions.
If the determined leadframe tips are judged to be outside of the ranges of the design conditions (YES) at step S5-2, the process returns to step S4-4, where the center of the circle which determines where to dispose the leadframe is moved to change the leadframe tip interval. If the determined leadframe tips are judged not outside of the ranges of the design conditions (NO), the process goes to step S7, where it is judged whether the determined leadframe tips satisfy the design criteria. If the determined leadframe tips satisfy the design criteria (YES) at step S7, design results are displayed at step S8. If the determined leadframe tips do not satisfy the design criteria (NO), the process returns to step S4-2 to reset the leadframe tip width.
The above conventional method has a disadvantage that a plurality of arrangement lines such as a cavity line need to be input as design conditions. Further, since the leadframe tip width and interval are determined according to the same criterion, pertaining to a circle radius, it is difficult to provide optimum values independently for the lead frame tip width and interval.
As described above, in the conventional leadframe tip arrangement method, it is difficult to determine a cavity line where leadframe tips are located. As a result, designing takes a long time and design results vary to a large extent from one designer to another. Further, the conventional method has the disadvantage that the leadframe tip width and interval cannot be set independently because they are determined according to the same criterion (same radius). This is a significant limitation on the flexibility of this design method.